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Abstract: In a typical industrial catalyst, a small amount of catalytically active species is finely dispersed inside a large amount of porous support material. The reactor volume is mainly occupied by the catalyst support, not by the catalytic species itself. The use of fluidised nanoparticles as catalyst without the need of a support may result in drastic reduction in catalytic reactor volume for major savings in capital and operating costs. Here we report for the first time the use of fluidised NiO nanoparticles to catalyse ethane–oxygen reaction at temperatures of 240–420°C. Our data indicate that the fluidised NiO nanoparticles exhibit very different characteristics from the traditional porous catalyst. The lack of a rigid porous structure in the fluidised NiO nanoparticle catalyst allows ethyl radicals to desorb from the catalyst surface into the gas phase to initiate further gas-phase radical chain reactions. Therefore, the ethane–oxygen reaction catalysed by the fluidised NiO nanoparticles shows some typical behaviour of gas-phase reactions. In contrast, the rigid porous structure in the NiO/SiO2 catalyst does not allow the radicals to desorb from catalyst surface into the bulk gas phase. [Copyright &y& Elsevier]

Abstract: The reduction of solid metal oxide by hydrogen or hydrocarbon gases represents a class of reactions that are important to various technological applications. This study investigates the reduction of unsupported NiO nanoparticles and silica-supported NiO with different reducing gases (hydrogen, methane and ethane) in the temperature range of 500–600°C. It was found that, in addition to the reaction and mass transfer of molecular species, the fates and activities of surface-formed radical species have to be considered in explaining the kinetics of nickel oxide reduction. It is believed that the desorption of hydrocarbon radicals from the particle surface has significantly slowed down the reduction of unsupported NiO nanoparticles. The ease with which a radical migrates from its generation site on a metallic island to the Ni–NiO surface boundary, on the other hand, is an important rate-determining factor in the reduction of silica-supported NiO. [Copyright &y& Elsevier]